Hello Adam, as former engineer of STS may I can help you. This error means that the PC does communicate with the modeles eg. VAC, PFC etc First switch of the 24V power supply for the tool and turn back on after 20 sec to restart the modules. Second restart the PC software. If the problem occurs again the shut down the process software agian and start the diagnostic program. It may tell you which of the modules of the seriel loop does not respond. Best regards Mit freundlichen Grüßen André Hiess, Technologieberatung-Service-Schulung Gmünder Str.4, 01279 Dresden, Germany phone: +49 (0)351 2523577 mobile: +49 (0)1632581847 mail to: hiess1@aol.com